An electrode designed like a pomegranate – with silicon nano-particles clustered like seeds in a tough carbon rind – overcomes obstacles in using silicon for a new generation of lithium-ion batteries, claim inventors.“This design brings us closer to using silicon anodes in smaller, lighter and more powerful batteries,” said Yi Cui, an associate professor at Stanford University and the Department of Energy’s SLAC National Accelerator Laboratory.

Experiments showed our pomegranate-inspired anode operates at 97 percent capacity even after 1,000 cycles of charging and discharging – which puts it well within the desired range for commercial operation, he added. The anode, or negative electrode, is where energy is stored when a battery charges. Silicon anodes could store 10 times more charge than the graphite anodes in today’s rechargeable lithium-ion batteries.

But there is a problem. The brittle silicon swells and falls apart during battery charging. Over the past eight years, Cui’s team has tackled the breakage problem by using silicon nanowires or nanoparticles that are too small to break.

In new study, researchers used a technique common in the oil, paint and cosmetic industries to gather silicon yolk shells into clusters. They coated each cluster with a second, thicker layer of carbon. Lab tests showed that pomegranate anodes worked well when made in the thickness required for commercial battery performance. The team is now working on to simplify the process and find a cheaper source of silicon nano particles.

One possible source is rice husks. They are unfit for human food and could be transformed into pure silicon nanoparticles relatively easily, said the research published in the journal Nature Nanotechnology.